(NewsCore) - Police discovered a mummified body in the passenger's seat of a southern California woman's car and say she had been driving round for months with it in the vehicle, The Orange County Register reported Thursday.

The body -- which has not yet been identified -- had withered to about 30 pounds when it was discovered by Costa Mesa police Monday after they responded to a call that a 1997 Mercury Marquis was parked illegally and was blocking a driveway.

Police said they smelled a foul odor coming from the car and after breaking a window to get inside saw a leg sticking out from under a pile of clothing.

The dead woman is understood to have been a transient aged between 50 and 60 years old and had been befriended by the driver of the car -- identified only as a 57-year-old former real estate agent.

She said she had found the body in the car -- registered to her ill father -- some months ago and was too afraid to report it to authorities. She had allowed the homeless woman to sleep in the car and the last time she saw her alive was in December.

Police said they believe the homeless woman had been dead for between three and 10 months, with the lack of air inside the car and weather conditions contributing to the preservation of the body.

Police found a box of baking soda in the car that had been used to try to mask the smell.

The cause of death was unknown but an autopsy revealed no obvious signs of foul play.